1. Field of the Invention
The present invention relates to a fuel tank for a motorcycle, and a process for producing the same.
2. Description of the Related Art
A conventional fuel tank for a motorcycle includes a body panel forming a main body of the tank, and a bottom plate which occludes an opening at a lower end of the body panel and whose outer surface is recessed inwards of the panel. A first junction flange portion which is integrally formed on a peripheral edge of the opening at the lower end of the body panel and a second junction flange portion which is integrally formed on an outer peripheral edge of the bottom plate are superposed on each other and seam-welded to each other over their entire peripheries. A structure in which the flanges are bonded by the seam-welding, has an advantage that a higher air tightness can be provided between the body panel and the bottom plate to enhance reliability. Moreover, the welding operability can be improved. The reason why the bottom plate is recessed inwards of the body panel (i.e., inwards of the tank), is that when the fuel tank is supported on a vehicle frame of the motorcycle, interference between the tank bottom and the vehicle body is avoided.
The conventional structure suffers from the following problem: Both of the first junction flange 2f' of the body panel 2' and the second junction flange 3f' of the bottom plate 3' are formed, turned downwards, and protrude prominently downwards from the bottom surface of the tank body 1', as shown in FIGS. 8A and 8B. For this reason, poor appearance results in a degraded marketability. Also, space occupied by the tank itself is increased by an amount corresponding to the protrusion of the junction flanges 2f' and 3f'.